Rare earth-based upconversion nanophosphors (UCN), as one of the new generation of bioluminescence labels, have advantages of good light and chemical stability, narrow absorption and emission bands, long luminescence life, and reduced risk of potential bio-toxicity and the like, compared to downconversion luminescence labels such as organic fluorescent dyes, quantum dots, and the like. Upconversion luminescence labels have great advantages such as deeper optical penetration depth, no fluorescence interference caused by biological background, and almost no harm to tissues due to the use of near infrared continuous laser as excitation source, which make it an ideal label for biological imaging. Further, since rare-earth upconversion nanomaterials are rare earth nanoparticles doped with fluorides, they have lower phonon energy, and may reduce non-radiative transition and increase luminescence intensity. Accordingly, among various substances such as oxides, sulfides, phosphides and the like, UCN has recently been widely used for analytic detection and the treatment of diseases and the like.
However, the use of rare-earth upconversion nanoparticles, as inorganic nanoparticles, for in vivo application and clinical test, may lead to many problems. For example, the nanoparticles are prone to agglomeration and not soluble in water, and thus can not be used in in vivo environment; when used for in vivo biological imaging and photodynamic therapy, the nanoparticles may non-specifically attach to a number of tissues, cells, and biomolecules, which may affect the effects to be obtained; when they are introduced into cells or animal bodies, the nanoparticles may result in serious autophagy of cells, or even death of cells and the like.
Recently, the surface modification of inorganic nanoparticles is mainly achieved in a covalent and non-covalent way, by using silica gel (CN101434748), fatty acids (CN1400167), PEG (CN101038290), chitosan (CN101411893), proteins, polypeptides, and the like to modify the surface characteristics of nanoparticles. Among others, the method of coating with a specific binding peptide is a preferred method for surface modification. The method results in significant multifunctionality, biocompatibility, simplicity, and expansibility. Recently, the specific-binding polypeptides, which are mainly reported nationally and internationally, are mainly binding to tissues, organs, cells, and proteins in vitro or in vivo. Examples of such polypeptides are polypeptides specifically binding to normal or cancerous tissues and organs (CN101531706, CN101827583A, CN1563078, CN102060909A, CN101891803A); polypeptides specifically binding to normal or cancerous cells (CN101918433A, CN1709905, CN1763082, CN101033251, CN1900108); and polypeptides specifically binding to proteins in vivo (CN102060913A, CN1823087, CN1262688, CN102105487A, CN101146822, CN1721432, CN1687128, CN101225108, CN101113164, CN101481418). However, polypeptides specifically binding to inorganic nanoparticles have been rarely reported. Only reported are polypeptides specifically binding to titanium, silver, and silicon (CN1829734) and polypeptides binding to nickel with high affinity (CN1911956).
Further, a common biological effect in nanomaterials has been discovered in recent studies, i.e., when they are introduced into cells, nanomaterials result in an abnormally increased level of autophagy of the cells. Cell autophagy is a stress response of cells to outside stimulation such as deficiency of nutrients and the like, in which a double-layer membrane structure is formed to encapsulate part of cytoplasm and organelles into autophagosomes which then fuse with lysosomes to form autophagy lysosomes, in which the contents are digested and reused. Therefore, the cell autophagy caused by nanomaterials is a double-edged sword. With the quick development of nano-technology, an increasing number of nanomaterials are introduced into human body with or without intention. Potential autophagy probably caused by these nanomaterials may have safety risks on human health. In addition, autophagy is closely associated with the occurrence and development of severe diseases. Regulation of autophagy caused by nanomaterials widely used for biomedical diagnosis and treatment may facilitate the use of nanomaterials for the diagnosis and treatment of diseases such as cancer.
Recently, the studies on the regulation of autophagy are mainly focused on the regulation of the level of autophagy per se. For example, autophagy revulsants, Dihydroartemisinin (CN102038678A), the complexes of manganese with dipicolylamine ligands targeting mitochondrion (CN101392007), 4-benzothiopheneaminoquinazoline derivatives (CN101836992A), β-carboline ruthenium complex (CN101845060A), plant viruses (tobacco mosaic virus) (CN101653462), rapamycin (CN102274219A), nonreceptor tyrosine kinase c-Abl specific inhibitor (CN1899616), hydroxytyrosol (CN102397268A); and some autophagy inhibitors, Bafilomysin A1 (CN101953845A), 3-methyladenine, SB203580, LY294002, or wortmannin (CN101869568A), chloroquine (CN101920015A), hydroxychlorquine (CN101428025) are used. However, no study on the regulation of autophagy caused by inorganic nanomaterials has been reported.
Therefore, there is an urgent need for the development of polypeptides able to specifically bind to rare-earth nanoparticles, and for the development of a method of regulating (including increasing and reducing) autophagy and toxicity caused by the use of rare-earth nanomaterials (especially, upconversion nanomaterials) in vitro and in vivo.